Almost as big as a minibus, it left its misshapen footprints at the bottom of a pond 129 million years ago.
About 129 million years ago, an unknown dinosaur that an adult man would not reach even the hips and almost as long as a minibus wandered in a strange way through what is now the Cuenca mountain range. The beast, which is only known to be a carnivorous theropod, the largest in the area, probably suffered from a deformity in one of the two legs on which it walked. When crossing a pond, he left unusual footprints that have been examined by a team coordinated by paleontologists from the Autonomous University of Madrid (UAM). The findings, published in PLOS ONE, are the result of work that could be described as detective work.
When scientists working at the Las Hoyas site discovered the trail of six footprints of a bipedal dinosaur, they soon became aware of its exceptionality.
They observed that the marks on the right foot were 45 cm long and showed all three toes, while those on the left foot were shorter about 35 cm, and the innermost toe was barely visible, which seemed to indicate a malformation, such as if it were curved inward. In addition, the footprints were more widely spaced than would be expected, suggesting that this dinosaur adjusted its stride to compensate for its injured foot. The depth and certain toenail marks of the right footprints support the idea that the animal was putting more weight on that side, as if it had a slight limp, although it was able to support both legs.
“It was a challenge to find out what was going on. We had to debate and rule out many things, that there were not two dinosaurs or that the sediment had a different consistency,” Angela D. Buscalioni, professor at the Department of Biology and Paleontology at the UAM and director of the Center for Integration in Paleobiology (CIPb-UAM).
Like the pigeons
Interestingly, similar deformities are seen in the toes of birds, something well known to pigeon keepers and not so hard to spot in city parks. Birds with these conditions have wide splayed legs and similar compensatory behaviors in their movements.
The identity of the dinosaur to which those footprints belonged is still a mystery. “We know what it is not, but we don’t know what it is,” says Buscalioni. The size of the footprints surprised the scientists, as they were much larger than those of two famous Las Hoyas dinosaurs: Pelecanimimus, which resembles an ostrich, or Concavenator, with a distinctive hump on its back. This indicates that the mysterious dinosaur, of a species not yet discovered, could overshadow them. The height of the animal to the hip must have reached two meters and easily reached six or seven in length. That was already extraordinary in itself. “After 30 years of excavations in Las Hoyas, finding evidence of the existence of a new species and in addition to that size is something impressive,” says the researcher.
The dinosaur left its footprints by stepping on a microbial mat at the bottom of a pond whose milky-looking waters were probably foul-smelling. At that time, the Iberian Peninsula was actually an oceanic island located in the Tethys Sea, between Eurasia, America, and Africa, and in the current Cuenca mountain range, there was an ecosystem of wetlands teeming with life. There have been recorded from algae, insects, and fish to birds, mammals, and dinosaurs. “Las Hoyas is the complete photograph of a moment,” says Buscalioni. Now, the appearance of large spaces with a large number of footprints further expands the margins of that snapshot. “We keep working because we know that under some layers we will find more traces,” he announces.
Able to survive
It is impossible to know what the lame dinosaur was doing there, whether it had come to the pond to drink or was hunting in the surrounding area. In those waters, there were hundreds of fish, so it could not be ruled out that they fed on them as it is confirmed that other dinosaurs did, although, for now, that remains in the field of speculation. “We think that the animal did not live in that area but that it crossed through there at a time of seasonal change,” he adds. What is “a surprise”, points out the researcher, is that a dinosaur of that size was able to survive, hunting or feeding on carrion, and become an adult despite its defect.
